Wireless sensor networks (WSNs) are gaining worldwide popularity due to their broad applications in different environments, including office, home, and hostile areas. Such WSNs may present a meaningful and efficient solution to challenging problems, such as building safety monitoring, vehicle tracking, wildlife tracking, and environmental surveillance. Advances in micro electromechanical system technology (MEMS), combined with radio frequency (RF) circuits and low cost, low power digital signal processors (DSPs), improve feasibility of these sensor networks.
A WSN may consist of multiple sensors that sense data of interest and transmit the sensed data, directly or indirectly, to a remote database for further processing. The sensors in the WSN are usually power constrained and have limited computational and communication power. Therefore it may be desirable to maximize lifetime of the sensors under this constraint. The lifetime of the sensors depends on effective energy saving strategies such as sensor scheduling and in-network information processing to reduce the amount of sensed data transmitted to a remote database.
One exemplary in-network information processing technique is data aggregation, which has been utilized as a paradigm for wireless routing in sensor networks. Since sensors are usually energy constrained, it may be inefficient and power consuming for all of the sensors to transmit sensed data directly to a remote database for processing. Data sensed by neighboring sensors is often highly correlated and hence redundant. In addition, the amount of the sensed data in a WSN of large size is usually very large for a remote database to process. Data aggregation is a technique that can aggregate data at neighboring sensors or intermediate sensors, which may reduce the amount of the sensed data transmitted to the remote database. As a result, data aggregation can save energy and improve bandwidth utilization for the WSN.
FIG. 1 illustrates a conventional clustered WSN 100. With reference to FIG. 1, the WSN 100 includes non-overlapping clusters 102-1, 102-2, . . . , 102-N (N is the total number of clusters in the WSN 100) with a fixed aggregator or cluster head 104-1, 104-2, . . . , 104-N in each cluster. Each sensor 106-1, 106-2, . . . , 106-M (M is the total number of sensors in the WSN 100) senses certain parameters, such as temperature, pressure, or humidity, of an environment, and encrypts sensed data. Each sensor 106-1, 106-2, . . . , 106-M then transmits its encrypted data to the one of the fixed aggregators 104-1, 104-2, . . . , 104-N in its own cluster. Each fixed aggregator 104-1, 104-2, . . . , 104-N may receive and decrypt the encrypted data received from different sensors in its own cluster and aggregate the decrypted data. Each fixed aggregator 104-1, 104-2, . . . , 104-N may then encrypt the aggregated data and wirelessly transmit the encrypted and aggregated data to a remote database 108 for further processing.
While data aggregation can help improve bandwidth utilization and conserve energy resources by reducing data redundancy, fixed aggregators are usually needed to perform data aggregation. When fixed aggregators perform aggregation of encrypted data received from different sensors in their own cluster, the fixed aggregators may need to decrypt the encrypted data before data aggregation. As a result, security issues may exist in WSNs including such fixed aggregators. Such security issues include data secrecy and data privacy. In terms of data secrecy, sensed data should be protected from attacks, such as known-ciphertext attacks, known-plaintext attacks, and relay attacks, during data transmission. In terms of privacy, sensed data should remain secret to the fixed aggregators. For example, each fixed aggregator 104-1, 104-2, . . . , 104-N should not know the contents of the sensed data received from any of the sensors 106-1, 106-2, . . . , 106-M in its own cluster.
In addition, sensors and aggregators in a conventional clustered WSN like the WSN 100 are usually in fixed positions once the conventional clustered WSN is deployed. New sensors or aggregators may not be added to, and existing sensors or aggregators may not be removed from, the conventional clustered WSN.